Include scroll snap in scroll position used for sticky offset calculation.

cc/trees/property_tree.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 
 #include <set>
 #include <vector>
 
 #include "base/logging.h"
@@ skipping 406 matching lines @@
   if (node->sticky_position_constraint_id == -1)
     return gfx::Vector2dF();
   const StickyPositionNodeData* sticky_data =
       tree->StickyPositionData(node->id);
   const LayerStickyPositionConstraint& constraint = sticky_data->constraints;
   ScrollNode* scroll_node =
       tree->property_trees()->scroll_tree.Node(sticky_data->scroll_ancestor);
   gfx::ScrollOffset scroll_offset =
       tree->property_trees()->scroll_tree.current_scroll_offset(
           scroll_node->owner_id);
+  gfx::PointF scroll_position(scroll_offset.x(), scroll_offset.y());
+  // The scroll position does not include snapping which shifts the scroll
+  // offset to align to a pixel boundary, we need to manually include it here.
+  scroll_position -= tree->property_trees()
+                         ->transform_tree.Node(scroll_node->transform_id)
+                         ->scroll_snap;
 
   gfx::RectF clip(
-      gfx::PointF(scroll_offset.x(), scroll_offset.y()),
+      scroll_position,
       gfx::SizeF(tree->property_trees()->scroll_tree.scroll_clip_layer_bounds(
           scroll_node->id)));
   gfx::Vector2dF sticky_offset(
       constraint.scroll_container_relative_sticky_box_rect.OffsetFromOrigin());
   gfx::Vector2dF layer_offset(sticky_data->main_thread_offset);
 
   // In each of the following cases, we measure the limit which is the point
   // that the element should stick to, clamping on one side to 0 (because sticky
   // only pushes elements in one direction). Then we clamp to how far we can
   // push the element in that direction without being pushed outside of its
@@ skipping 1892 matching lines @@
 
   const EffectNode* effect_node = effect_tree.Node(effect_id);
 
   bool success = GetFromTarget(transform_id, effect_id, transform);
   transform->Scale(effect_node->surface_contents_scale.x(),
                    effect_node->surface_contents_scale.y());
   return success;
 }
 
 }  // namespace cc